Duplex fuel nozzle



Feb. 1, 1955 W. J. PURCHAS, JR., ETAL DUPLEX FUEL NOZZLE Filed April 26, 1951 United States Patent DUPLEX FUEL NOZZLE William J. Purchas, Jr., and Edward Orent, Grand Rapids,

Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 26, 1951, Serial No. 223,061

4 Claims. (Cl. 299-115) Our invention relates to fluid spray nozzles, and particularly to nozzles of a character suited for use as fuel nozzles in gas turbine combustion chambers.

Gas turbine combustion systems, particularly those of aircraft engines, are highly exacting in their requirements for fuel nozzles. Because of the high air velocity through the combustion chambers and the limited size of the combustion apparatus, a very high standard of atomization of the fuel must be attained to promote good combustion. The difficulty of securing consistently good atomization of the fuel and a good spray pattern, both of which are necessary for proper combustion, is greatly increased by the great range of fuel requirements of aircraft jet engines and the like. The overall range of fuel fiow is commonly of the order of thirty to one.

The most satisfactory results have been obtained with nozzles of the type in which the fuel is forced under considerable pressure tangentially into a swirl chamber and emerges through an outlet orifice on the axis of the swirl chamber. Since the fiow in such a nozzle is proportional to the square root of the pressure drop across the swirl ports, a flow range of thirty to one represents a pressure range of nine hundred to one. No direct way has been found to secure proper atomization over such a range with a single set of swirl ports. This difiiculty has led to proposals to bleed off or bypass fuel from the swirl chamber. Systems based on this principle are complicated and have not been found to be particularly satisfactory. A more successful approach to the problem of securing adequate flow range lies in the provision of two sets of swirl ports, a set of small capacity and a set of large capacity, the latter being brought into use when the flow approaches the capacity of the small ports.

Systems employing such duplex nozzles may include a valve in each nozzle to distribute the flow from a single fuel inlet between the small and the large swirl ports, as shown in U. S. Patents 1,873,781, Nightingale, or 2,628,867, Purchas, or may be of a type in which the supplies to the small and large ports of each nozzle are independent, so far as the nozzle is concerned, the large ports being supplied under control of an external valve or other regulating mechanism.

Although operating experience with the duplex nozzle has been favorable as compared to other systems, certain faults have existed in such nozzles. One such fault has been that fuel supplied through the small swirl ports has backed up through the large flow ports. Depending upon the character of the system, this back pressure in the large flow supply line may adversely effect the operation of the valves which control flow to the large ports, or, if the large flow inlet lines are connected to a common manifold, fuel supplied through the small flow ports may transfer from one nozzle to another through this large flow manifold. In either case, the result may be inequalities in flow between the nozzles, which adversely affects combustion and performance of the engine at low fuel flows.

Also, at rates of fiow at which the large fiow ports are supplied with fuel at a rate small in comparison to the capacity of these ports, difiiculty has been experienced in obtaining good atomization of the fuel supplied through the large swirl ports.

The principal objects of the present invention are to provide a fuel nozzle with superior atomization characteristics over a wide range of flow; to provide a fuel nozzle of the duplex type in which bleeding of fuel supplied through the small swirl ports into the supply lines for the large ports is inhibited; to provide a duplex nozzle in ice which the volume of the swirl chamber supplied by the small ports is not adversely effected by the presence of the large ports; and to provide a fuel nozzle of the duplex type in which atomization of the fuel supplied through the large flow ports at small rates of flow therethrough is assisted by the kinetic energy of the fuel supplied through the small flow ports.

Other objects of the invention are to provide a fuel nozzle resistant to the adverse operating conditions obtaining in a gas turbine combustion chamber or the like, and to provide a fuel nozzle of the character indicated which is simple and rugged in structure and may be easily manufactured with economy and precision.

This application is a continuation-in-part of our copending application for Duplex Nozzle, Serial No. 132,864, filed December 14, 1949.

The nature of the invention and the advantages thereof will be clearly apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings.

Figure 1 is an axial sectional view of the discharge end of a fuel nozzle in accordance with the invention; Figures 2 and 3 are cross-sectional views taken on the planes indicated in Figure l; and Figure 4 is a partial elevation view of the nozzle cap.

Referring to Figure 1, the nozzle comprises a body 10 including a shank 11 adapted to be mounted in a gas turbine engine so as to extend into the combustion air supply duet thereof and an end portion 12 which may-extend axially of the duct. The body 10 is bored and threaded as indicated at 13 to receive the nozzle cap 14 within which is mounted the structure comprising swirl chambers and swirl ports by which the spray is established. This last mentioned assembly, which may be termed the nozzle tip or spray tip, is indicated generally at 16. It comprises an annular body which seats against an inwardly directed flange 17 on the nozzle cap 14 and is piloted within the flange 17. The spray tip assembly 16 is held in place by a collar 18 which is forced against the assembly by a plug 19 and a jam nut 21, the members 19 and 21 being received in the threaded portion 22 of the nozzle cap 14. Themembers 18, 19, and 21 are provided with intercommunicating internal passages by which fuel is supplied to the large flow ports of the spray tip 16. This fuel enters through passages 23 and 24 in the body of the nozzle which communicate with an external source (not shown). The lower end of the passage 23 is closed by a plug 26 after the passage is drilled.

Fuel for the small flow ports of the nozzle is supplied to drilled passages 27 and 28 in the nozzle body from a suitable source (not shown) to the inner end of the threaded bore in the body portion 12 in which the nozzle tip 14 is seated. It may be noted that the nozzle tip seats precisely against the face 29 of the body and that an annular groove 31 is formed in the inner face of the nozzle cap to receive fuel supplied to the passage 28. From the groove 31 the fuel is conducted through a drilled passage 32 in the nozzle tip to an annular chamber 33, 34 disposed around the spray tip assembly 16. Referring to Figures 1, 2, and 3, the spray tip assembly 16 comprises an annular hollow body provided with a flange 36 which is clamped between the collar 18 and the flange 17 of the nozzle cap. The body is formed to define a small flow swirl chamber 37 which converges toward a spray outlet orifice 38, the discharge end of which is chamfered. Two swirl ports 41 entering the swirl chamber 37 tangentially conduct fuel from the chamber 34 into the swirl chamber 37. The large flow swirl ports 42 (Figures 1 and 2) are directed tangentially through the wall of the spray tip body 16, and conduct fuel from an annular chamber 43 in the collar 18 to the large flow swirl chamber 44. The inner end of the large flow swirl chamber 44 is closed by a disk 46 which may be pressed or brazed in place.

The swirl chambers are separated by an orifice plate 47 of generally conical form which is pressed into place against a shoulder in the nozzle tip 16. Fuel introduced through the large flow ports 42 swirls in the chamber 44 and escapes through an orifice 48 in the plate 47 into the small flow swirl chamber 37 and out through the spray orifice 38. It will be noted that the orifice 48 is of somewhat smaller diameter than the orifice 38.

The operation of the nozzle as thus far described is as follows: Assuming that the engine in which the nozzle is installed is being started or is operating under low fuel demand conditions, fuel is supplied only through the passages 27, 23, and 32 and the small flow ports 41. The fuel thus introduced under substantial pressure escapes through the orifices 41 at high velocity, develops a high circumferential velocity in the swirl chamber 37, and spills out over the lip of the spray orifice 38. Since this orifice is of larger diameter than the orifice 43, centrifugal force keeps the rotating body of fluid in the swirl chamber at a greater radius than that of the orifice 48, so that the fuel does not flow back through the orifice 48 into the large flow system.

If the demand for fuel approaches a value beyond the capacity of the ports 41, additional fuel is supplied through the passages 23, 24 and the members 21, 19, and 13 to the chamber 43, from which it fiows through the ports 42, establishing a swirl in the chamber 44. Centrifugal force urges the fluid against the outer wall of the swirl chamber and it spills over through the orifice 48 into the swirl chamber 37, where it mingles with and is accelerated by the fluid swirling at higher velocity in the low flow chamber. The fluid escaping through the orifice 48 thus mingles with that given a high rotational velocity by fiow through the ports 41, and the joint flow from the two sets of ports escapes tangentially over the lip of the spray orifice 38. This mingling of the fluids greatly improves the spray pattern in the transition zone of flow between flows which are within the capacity of the small flow ports and those which are sufiiciently great to establish a high swirl velocity in the large flow swirl chamber 44. The small flow ports preferably remain in operation regardless of the fiow rate, increased fuel demand being supplied by both sets of ports up to the capacity of the nozzle.

It will be noted that the large flow swirl chamber is greater both in diameter and in axial length than the small flow swirl chamber, the form and position of the orifice plate 47 being such that the small flow chamber is held to the size best suited for its operation. Thus. the provision of an adequate swirl chamber for the large flow does not impair the performance of the small flow swirl chamber.

The proportions of the parts as illustrated in the drawings are based on those of an actual nozzle for an aircraft gas turbine engine, Figure 1 being approximately two and one-half or three times the scale of the actual nozzle. It will be understood, of course, that the dimensions of the nozzle and more particularly the size of the swirl chambers and the orifices 38 and 48 and the size and number of the swirl ports will vary with the fuel demand of the installation for which a particular nozzle is intended. These values will also depend to some extent upon the nature of the fuel supply system. The particular nozzle illustrated in the drawings is intended for a system in which the means for closing off the supply to the large flow ports at low rates of flow, and apportioning flow between the two sets of ports at large rates, imposes a considerable pressure drop on the supply to the large flow ports. Therefore, these ports are larger in proportion to the small flow swirl ports than they would be if the system were such to provide equal pressure to both sets of ports.

The nozzle is provided, in addition to the structure for spraying the fuel, with an arrangement for supplying a controlled quantity of air to the vicinity of the spray outlet 38, this air serving to cool the nozzle and minimize deposition of carbon from the fuel.

Referring to Figures 1, 2, and 4, the nozzle cap 14 comprises a cylindrical portion 51 in which are cut a number of helical grooves 52. A portion of the cap is also formed with flats 53 for application of a wrench to screw it into the nozzle body. The nozzle body is externally threaded as indicated at 54 to receive a shroud 55 which engages a shoulder on the body for axial location. The shroud 55 is formed with a number of air inlets 56 which communicate with the interior of the shroud 54. Air flows through the openings 56, between the shroud and the nozzle cap, through the helical groove 52, which imparts swirl to the air, and inwardly through the space 57 between the end of the nozzle cap and an inwardly directed flange 58 of the shroud to be discharged adjacent the discharge end of the spray tip 16. It will be noted that the shroud is formed with a shoulder 61. In the installation of the nozzle, the portion of the shroud to the right of the shoulder in Figure 1 extends into the combustion chamber flame tube or combustion liner and the portion to the left of the shoulder is in the air supply duct to the combustion chamber. Due to the pressure differential between the outside and inside of the combustion chamber flame tube, air flow is set up through the passages thus described providing a small supply of air through the nozzle to cool the nozzle and reduce carbon formation.

The installation and environment of the nozzle in a gas turbine combustion chamber is not further described, since such installations are well known to those skilled in the art, and a further description thereof is not required for an understanding of the invention.

The advantages of the invention will be apparent to those skilled in the art from the foregoing. The invention is not to be considered as limited by the detailed description of the preferred embodiment thereof, as many variations thereof may be devised by skill in the art within the scope of the principles of the invention.

We claim:

1. A spray nozzle comprising, in combination, a body, means defining a swirl chamber in the body converging to a spray outlet orifice, first swirl port means for supplying liquid tangentially to the swirl chamber, second swirl port means of larger capacity than the first swirl port means for supplying liquid tangentially to the swirl chamber at a zone farther removed from the outlet orifice than the first swirl port means, and an orifice plate mounted in the swirl chamber between the first and second port means, the orifice plate being provided with an orifice therein coaxial with the swirl chamber and smaller in diameter than the outlet orifice, the spacing of the said orifices axially of the chamber being sufficiently great that liquid supplied through the second swirl port means and discharged through the orifice plate is intercepted by the means defining the swirl chamber.

2. A spray nozzle comprising, in combination, a body, means defining a swirl chamber in the body converging to a spray outlet orifice, first swirl port means for supplying liquid tangentially to the swirl chamber, second swirl port means of larger capacity than the first swirl port means for supplying liquid tangentially to the swirl chamber at a zone farther removed from the outlet orifice than the first swirl port means, and a generally conical orifice plate mounted in the swirl chamber between the first and second port means, the orifice plate converging toward the outlet orifice and being provided with an orifice therein coaxial with the swirl chamber and smaller in diameter than the outlet orifice, the spacing of the said orifices axially of the chamber being sufficiently great that liquid supplied through the second swirl port means and discharged through the orifice plate is intercepted by the means defining the swirl chamber.

3. A spray nozzle comprising, in combination, a body, means defining first and second coaxial adjacent swirl chambers therein, a plate between the swirl chambers defining an orifice for discharge of liquid from the first into the second swirl chamber, means defining a spray outlet orifice for discharge of liquid from the second swirl chamber, the said orifices being coaxial with the swirl chambers and the outlet orifice being of larger diameter than the orifice in the plate, and means including tangential liquid inlet port means for supplying liquid to each swirl chamber, the inlet means of the first swirl chamber being of larger capacity than that of the second swirl chamber, the spacing of the said orifices axially of the chambers being sufiiciently great that liquid supplied to the first swirl chamber and discharged through the firstmentioned orifice is intercepted by the means defining the second swirl chamber.

4. A spray nozzle comprising, in combination, a body, means defining first and second coaxial adjacent swirl chambers therein, a conical plate between the swirl chambers converging toward the second swirl chamber and defining an orifice for discharge of liquid from the first into the second swirl chamber, means defining a converging spray outlet orifice for discharge of liquid from the second swirl chamber, the said orifices being coaxial with the swirl chambers and the outlet orifice being of larger diameter than the orifice in the plate, and means including tangential liquid inlet port means for supplying liquid to each swirl chamber, the inlet means of the first swirl chamber being of larger capacity than that of the second swirl chamber, the spacing of the said orifices axially of the References Cited in the file of this patent UNITED STATES PATENTS 1,066,161 Stilz July 1, 1913 6 Kestner Apr. 21, 1914 Nightingale Aug. 23, 1932 Goddard Mar. 6, 1951 Berggren Sept. 4, 1951 FOREIGN PATENTS Great Britain Aug. 2, 1946 

